Biodegradable polymeric compositions comprising starch and a thermoplastic polymer

ABSTRACT

The present invention provides polymeric compositions containing thermoplastic starch and a thermoplastic polymer incompatible with starch, in which the starch constitutes the dispersed phase and the thermoplastic polymer constitutes the continuous phase, selected: A) from compositions comprising an agent with an interfacial effect selected from esters of polyols with mono- or polycarboxylic acids with dissociation constants within certain limits, the esters having specific values of the hydrophilic/lipophilic balance index HLB or being amongst the non-ionic surfactants which are soluble in water but cannot significantly be extracted by water from the compositions which contain them; B) from compositions wherein the thermoplastic polymer is an aliphatic or aliphatic-aromatic copolyester wherein the ratio (R) between the average viscometric molecular weight and the melt index is greater than 25,000 and C) from compositions wherein the thermoplastic polymer is selected from aliphatic-aromatic copolyesters, polyester-amides, polyester-esters, polyester-ether-amides, polyester-urethanes and polyester-ureas and wherein the compositions are obtained by extrusion of the component maintaining a water content during the mixing stage from 1 to 5% by weight.

The present invention relates to biodegradable polymeric compositionswith good resistance to ageing and to low humidities, comprisingthermoplastic starch and a thermoplastic polymer incompatible withstarch. In these compositions, starch constitutes the dispersed phaseand the thermoplastic polymer constitutes the continuous phase.

The invention relates in particular to biodegradable compositions whichcan maintain a high tear strength in conditions of low humidity.

It is known that the mechanical properties, particularly the tearstrength, of products (films) produced from compositions comprisingthermoplastic starch and a thermoplastic polymer incompatible withstarch in which the starch constitutes the dispersed phase undergoconsiderable deterioration because the starch gives up or absorbs wateruntil it achieves equilibrium with the ambient humidity.

In conditions of relatively low humidity, for example 20% humidity, thematerial tends to become fragile since the dispersed phase becomesinsufficiently plasticized because of the loss of water which raises theglass transition point above the ambient temperature.

In these conditions, when the starch particles constituting thedispersed phase are stressed they cannot deform and absorb the stressbut remain rigid, thus initiating tearing.

Water is a very effective plasticizer of the starchy phase; however, ithas the disadvantage that it is volatile and that its concentrationfluctuates in order to achieve equilibrium with the ambient humidity.High-boiling plasticizers such as glycerol, sorbitol, etherified oresterified sorbitol, ethylene glycol, trimethylol propane,pentaerythritol and polyols in general are therefore preferred.

Some of the water present during the plasticizing of the starch issupplied by the starch itself and some may be added.

Upon completion of the plasticizing and the mixing of the components,the water is removed by degassing to give a final content of about 1–3%by weight.

Water, like high-boiling plasticizers, modifies the viscosity of thestarch phase and affects the rheological properties of thestarch/polymer system, helping to determine the dimensions of thedispersed particles.

The most effective high-boiling plasticizers (glycerol in particular)tend to be lost from the system either because of evaporation in aventilated atmosphere, particularly if the humidity undergoes cyclicvariations, or by migration in contact with other hydrophilic materialssuch as cellulose.

In both cases, the concentration of plasticizer is no longer sufficientto keep the Tg of the dispersed phase below the temperature of use andthe material becomes fragile.

To prevent this problem, plasticizers such as, for example, sorbitol,sorbitol mono-ethoxylate and trimethylol propane, which do not migrateand do not evaporate, have been used.

The effectiveness of these plasticizers, however, is quite low and thefinal characteristics of the material are worse than those obtained withthe use of more effective plasticizers such as glycerol, particularly inconditions of low humidity.

To prevent the problems which arise in dry conditions, it has also beenattempted to bring the Tg of the dispersed phase back to values belowthe temperature of use by increasing the quantity of high-boilingplasticizer. This gives rise to too soft a “feel” of the material whenit is in the 50% relative humidity conditions in which the material isnormally calibrated to achieve the maximum performance.

It has now unexpectedly been found that the problem of providingbiodegradable heterophase compositions comprising thermoplastic starchand a thermoplastic polymer incompatible with starch in which starchconstitutes the dispersed phase and the polymer constitutes thecontinuous phase capable of maintaining high mechanical properties evenin conditions of low relative humidity can be solved by using acomposition selected from the following ones:

A) Compositions prepared by extrusion of the components in the presenceof an interfacial agent selected from the group consisting of:

a) esters which have hydrophilic/lipophilic balance index values (HLB)greater than 8 and which are obtained from polyols and from mono- orpolycarboxylic acids with dissociation constants pK lower than 4.5 (thevalue relates to the pK of the first carboxyl group in the case ofpolycarboxylic acids);

b) esters with HLB values of between 5.5 and 8, obtained from polyolsand from mono- or polycarboxylic acids with less than 12 carbon atomsand with pK values greater than 4.5 (this value relating to the pK ofthe dissociation of the first carboxyl group in the case ofpolycarboxylic acids);

c) esters with HLB values lower than 5.5, obtained from polyols and fromfatty acids with 12–22 carbon atoms, used in quantities of from 10 to40% by weight relative to the starch;

d) non-ionic, water-soluble surfactants which, when added to thestarch/thermoplastic polymer heterophase compositions indicated above,migrate in water by no more than 30% of their concentration after thematerial containing them has been immersed in water for 100 hours atambient temperature;

e) reaction products of an aliphatic or aromatic diisocyanate with apolymer containing terminal groups reactive with the diisocyanates;

B) Compositions wherein the thermoplastic polymer incompatible withstarch is a polyester comprising repeating units deriving from analiphatic dicarboxylic acid and/or from a hydroxyacid with more than 2carbon atoms and wherein the ratio R between the average viscosimetricmolecular weight and the melt index of the polyester (measured at 180°C. under a load of 5 kg) is greater than 25,000;

C) Compositions wherein the thermoplastic polymer with starch is acopolyester selected from the aliphatic-aromatic copolyesters,polyester-amides, polyester-ethers, polyester-ether-amides,polyester-ureas, and polyester-urethanes, said compositions beingobtained by extrusion of the components under conditions wherein thecontent of water during the extrusion mixing is maintained from 1 to 5%by weight as measured at the exit of the extruder, prior toconditioning.

The HLB index of the ester a)–c) of the A) compositions is given by theratio between the molecular mass of the hydrophilic fraction of themolecule (Mh) and the total molecular mass (M) multiplied by 20:HLB=20×(Mh/M).

In the case of monoglycerides, the empirical formula normally adopted isthe following:

HLB=20 (1−S/A) in which S is the saponification number of the ester andA is the acidity number of the acid.

The hydrophilic/lipophilic balance of the esters is controlled by thelength of the acid chain and by the number of hydroxyl groups whichremain free after esterification.

The effect of the esters in bringing about compatibility in the case ofstarch/polyester systems is due to the interaction between the freealcohol groups of the ester and those of the starch and between theester groups of the ester which brings about compatibility, and thepolyester phase.

The esters of class a) are soluble in water; their effectiveness variesin dependence on the pK value of the acid and generally increases as thepK value decreases.

The best results are achieved with the esters of oxalic acid (pK=1.23),maleic acid (pK1=1.83), malonic acid (pK1—2.83), and mono-, di- andtri-chloroacetic acids (pK 2.83, 1.48 and 0.70, respectively).

Mono- and di-esters of polyols containing 3 or more alcohol groups arepreferred; mono- and di-glycerides, particularly of oxalic acid, areparticularly preferred. Mono- and di-esters of sorbitol, trimethylolpropane, pentaerythritol and similar polyols are also examples ofcompounds which can advantageously be used.

The esterification of the hydroxyl groups of the polyol is generallypartial, affecting between 10 and 90% of the hydroxyl groups, preferablybetween 20 and 70%, and most preferably between 25 and 50%.

The partial esterification condition applies both to the esters a) andto the esters b) and c).

The esters a) are generally used in a ratio to the starch of from 1:30to 1:2.5 by weight.

The quantities of the esters a) used are preferably from 5–40% relativeto the starch, or from 0.5 to 20% by weight relative to the totalcomposition. However, the compatibility effect starts to appear even atlevels of 1–3% of the total weight of the composition.

The esters are generally used to replace 30–35% of the plasticizer;however, they may also be used without plasticizers.

The HLB values of some monoglycerides of class a) and the pK1 and pK2constants of the corresponding acids are given by way of illustration:

Acid pK1 pK2 HLB of the ester Oxalic 1.23 4.19 12.4 Malonic 2.83 5.6911.7 Succinic 4.16 5.61 11.1 Adipic 4.43 4.41 9.9 Pivalic 4.78 — 8.4

The effect of the esters of type a) in bringing about compatibility issuch as to achieve a fine microstructure of the starch with a meanparticle size at least one order of magnitude smaller than that of theparticles of the compositions prepared, even in very favourablerheological conditions, in the absence of type a) agents for bringingabout compatibility.

The average numeral size of the starch particles is between 0.1 and 0.5microns and more than 80% of the particles have a size of less than 1micron.

The water content of the compositions during the mixing of thecomponents is preferably kept between 1 and 15% by weight.

It is, however, also possible to operate with a content of less than 10by weight, in this case, starting with pre-dried and pre-plasticizedstarch.

The fine microstructure of the starch permits the production of a filmwhich still retains good tensile and tear-strength properties afterwashing with water in order to remove the plasticizers. In these films,the small dimensions of the starch particles no longer enable tearing tobe initiated.

The esters of classes b) and c) are insoluble in water and are thereforenot removed by washing.

Unlike the esters which are soluble in water and which, as well asacting as interfacial agents, also have a fairly good plasticizingeffect, the insoluble esters, by virtue of the size of their hydrophobicaliphatic components, act mainly as interfacial agents, facilitating theslippage of the surfaces during stressing, thus minimizing the capacityof the particles, which have become rigid and no longer deformable as aresult of loss of plasticizer, to initiate tearing.

Examples of esters of class b) are monoglycerides of caproic acid(pK=4.85; HLB=7.3), of suberic acid (pK1=4.52 and HLB=6) and of azelaicacid (pK1=4.55 and HLB=5.8).

Esters of caproic acid, particularly monoglycerides (HLB=7.3), arepreferred since they can maintain a high tear strength of the filmswithout detracting from their quality.

Esters b) are generally used in a ratio to the starch of from 1:30 to1:2.5 or from 0.5 to 20% by weight relative to the total composition.

Examples of esters of class c) are monoglycerides of lauric acid (HLB5.4) and of oleic acid (HLB=4.2). Examples of other monoglycerides whichcan be used are those of myristic, palmitic, stearic, erucic andlinoleic acids.

The esters of class c), since materials of these types act asinterfacial agents and not as lubricants, are used in highconcentrations in comparison with those of the lubricants used in theprior art, that is, in concentrations of from 3 to 10%, preferably from5 to 10% by weight, which is equal to about 10–40% by weight relative tothe starch.

Examples of non-ionic surfactants of class d) are alkoxylatedalkylphenols with HLB indices greater than 10, such as nonylphenolethoxylate, with the degree of ethoxylation regulated in a manner suchthat the HLB is greater than 10.

The alkoxylated alkylphenols are used in concentrations within a fairlynarrow range, generally of from 3–7% of the weight of the composition.Concentrations outside this critical range have no effect. Otherexamples of surfactants of class d) are the ethoxylation products ofsorbitol, starch, fatty acids, rosinic acid, tall oil, amides of fattyacids and ethanolamides.

The acids usable in the preparation of the esters a) to c) comprisesaturated and unsaturated, linear or branched aliphatic and aromatic,mono- to polycarboxylic acids, possibly containing substituentsselected, for example, from halogen atoms, hydroxyl groups, alkoxylgroups, nitro groups, and ester groups, for example, acetyl citric acid.

Representative acids are:

formic acid, mono-, di- and tri-chloroacetic acid, propionic acid,butyric and isobutyric acids, amylic acid, isoamylic acid, pivalic acidand caproic acid, and fatty acids from lauric acid to docosanoic acid;

di-carboxylic acids such as oxalic, malonic, succinic, glutaric, adipic,suberic and azelaic acids;

hydroxy-acids such as glycolic, glyceric, lactic, citric, tartaric,malic, and benzoic acids, substituted benzoic acid and salicylic acid.

The interfacial agents of class e) are preferably obtained by reactionof a diisocyanate such as hexamethylenediisocyanate with analiphatic-aromatic polyester, such as poly-epsilon-caprolactone. Theagents e) are used in the amount of 1 to 10 by weight of thecomposition.

The polyols used for the preparation of esters a) to c) contain 3 ormore carbon atoms and 2 or more alcohol groups, for example, glycerol,di- and polyglycerols, ethylene or propylene glycol, ethylene orpropylene diglycol, polyethylene glycol, polypropylene glycol,1,2-propandiol, trimethylol ethane, trimethylol propane,pentaerythritol, sorbitol, erythritol, xylitol, sucrose, 1,3-propandiol,1,2-, 1,3-, 1,4-butandiol, 1,5-pentandiol, 1,6-, 1,5-hexandiol, 1,2,6-,1,3,5-hexantriol, neopentyl glycol, and polyvinyl alcohol prepolymers.

These polyols as such or esterified with acids other than those used inthe esters of classes a) and b) constitute an effective class ofplasticizers usable in the compositions of the invention.

Polyols usable as plasticizers, in addition to those indicated above,comprise polyol acetates, ethoxylates and propoxylates, particularlysorbitol ethoxylate, glycerol ethoxylate, sorbitol acetate, andpentaerythritol acetate.

These and other polyols which may be used are described in U.S. Pat. No.5,292,782.

The quantities of plasticizers used are generally from 1 to 100%,preferably from 10–30% by weight, relative to the starch.

The thermoplastic polymers incompatible with starch usable in the A)type compositions of the invention are preferably selected fromfollowing groups of polymers:

a) aliphatic polyesters obtained by polycondensation of hydroxy-acidswith 2 or more carbon atoms or of the corresponding lactones orlactides. Examples of these polyesters and their derivatives aredescribed in U.S. Pat. No. 5,412,005; polycaprolactones, hydroxy-butyricand hydroxyvaleric polymers and copolymers, polyalkylene tartrate, andglycolic and lactic acid polymers and copolymers are preferred;

b) aliphatic polyesters obtained by polycondensation of diols with 2–10carbon atoms with aliphatic dicarboxylic acids; polyalkylene succinate,polyalkylene adipate are preferred;

c) aliphatic polycarbonates such as polyethylene carbonate andpolypropylene carbonate, polyester-carbonates, polyamides-carbonates,polyesters amides-carbonates;

d) esters of cellulose such as cellulose acetate, cellulose propionate,cellulose butyrate and mixed esters thereof;

e) esters of starch such as starch acetate, propionate, and butyrate andstarches esterified with acids up to C18; the degree of substitution ofthe starch is between 0.5 and 3;

f) carboxymethyl cellulose, alkyl ethers and hydroxyalkyl ethers ofcellulose, polysaccharides, chitin and chitosan, alginic acid andalginates;

g) vinyl esters and copolyesters both as such and partially hydrolyzed,such as polyvinyl acetate, polyvinyl acetate-/polyvinyl alcohol up to50% hydrolysis, polyethylenevinyl acetate, polyethylene-acrylic acid andmixtures of polymers from a) to g).

The polyesters, particularly those obtained from hydroxy-acids, may bemodified to form block copolymers or graft copolymers with polymers orcopolymers which can react with the carboxyl and/or hydroxyl groupspresent in the polyesters.

The polymers and copolymers listed may be upgraded with chain extenderssuch as di- or polyisocynates, di- or polyepoxides, or withpolyfunctional compounds such as pyromellitic acid, pyromelliticanhydride.

The homopolymers and copolymers of epsilon-hydroxy-acids, particularly6-hydroxy-caproic acid and the corresponding lactone are preferred.

The polyesters and their derivatives generally have melting points ofbetween 40° and 175° C. and molecular weights (weighted average) greaterthan 20000, preferably greater than 40000.

The polyesters and their derivatives can advantageously be used inmixtures with one or more polymers or copolymers obtained fromethylenically unsatured monomers containing polar groups, preferablyhydroxyl and carboxyl groups, such as ethylene/vinyl acetate,ethylene/vinyl alcohol and polyvinyl alcohol copolymers (the latterobtained by hydrolysis of polyvinyl acetate and ethylene vinyl acetatecopolymers with degrees of hydrolysis of from 50 to 100%) andethylene/acrylic acid copolymers.

The ethylene/vinyl alcohol copolymers preferably contain from 10 to 50%by weight of ethylene.

The alcohol groups of the polymers mentioned above may be converted intoether, ester, acetal or ketal groups.

Preferred mixtures contain poly-epsilon-caprolactone and ethylene/vinylalcohol or ethylene/vinyl acetate or polyvinyl alcohol copolymers.

The ratio by weight between the polyesters and the polymers orcopolymers containing alcohol groups is preferably between 1:30 and30:1, more preferably between 1:15 and 15:1 and even more preferablybetween 1:6 and 6:1.

The ratio by weight between thermoplastic starch and e)–g) polymer isgenerally between 1:20 and 20:1 and preferably from 1:10 to 10:1, morepreferably from 1:4 to 4:1 and is selected in a manner such that thepolyester constitutes the continuous phase and the starch the dispersedphase.

Other preferred mixtures, used particularly in injection moulding,contain cellulose or starch esters with a degree of substitution ofbetween 1 and 3, particularly cellulose acetate and starch acetate.

The thermoplastic starch present in the compositions is obtained fromnative starch extracted from vegetables such as potatoes, rice, tapioca,maize and/or from chemically or physically modified starch.

The compositions of the invention may include quantities of from 0.5 to20% by weight of urea or hydroxides of alkaline-earth metals, between0.1 and 5% of inorganic salts of alkali-metals or alkaline-earth metals,particularly LiCl, NaCl, Na₂SO₄, and also compounds containing boron,particularly boric acid, proteins and salts of proteins such as casein,gluten, caseinates, etc., abietic acid and derivatives thereof, rosinicacids, and natural gums.

Other hydrophobic polymers such as polyethylene, polypropylene andpolystyrene and additives such as anti-oxidants, lubricants,flame-proofing agents, fungicides, herbicides, fertilizers andopacifiers, compounds with rodent-repellent effects, waxes andlubricants may be present.

The compositions are preferably prepared by mixing the components in anextruder heated to a temperature of between 100° and 220° C.

Instead of an extruder, the components may be mixed in any apparatuswhich can ensure temperature and shear stress conditions appropriate forthe viscosity values of the thermoplastic starch and of the polymerincompatible with starch.

The starch may be treated to render it thermoplastic before being mixedwith the other components of the composition or during the mixing of thecomponents of the composition.

In both cases, known methods are used, with operating temperatures ofbetween about 100° and 220° C., in the presence of plasticizers andpossibly water.

The water content at the output of the extruder (that is, before anyconditioning treatments) is preferably less than 5% by weight.

The content is regulated by degassing during extrusion or with the useof dehydrated starch with a low water content.

The compositions of the invention are usable particularly in thepreparation of films, sheets, fibres, in injection-moulding,thermoforming, coextrusion, and in the preparation of expandedmaterials.

Fields of use of particular interest are those of nappies and sanitarytowels, of films for agriculture particularly for mulching, of bags, offilms for cellophaning, of disposable articles, of expanded packagingelements, and of articles for nurserymen.

The films may be used in laminates with layers formed by polyesters,polyester-amides, polyamides, aliphatic polycarbonates,aromatic/aliphatic polycarbonates, soluble polymers such as polyvinylalcohol or other polymers, with paper, and with layers of inorganicmaterials such as silica, aluminium, etc.

The compositions may be supplemented with fillers, preferably of naturalorigin, and with natural or modified resins such as abietic acid.

The compositions of group B) contain as peculiar components a polyesterhaving a R ratio greater than 25,000 and preferably greater than 35.000and more preferably comprised between 35,000 and 110,000. Polyesterswith R ratios greater than 25,000 are preferably obtained by upgradingreaction, in the melt, of a polyester with a R ratio below 25,000 with abi- or polyfunctional compound having groups which are reactive withterminal OH and/or COOH groups of the polyester. The quantity of thepolyfunctional compound used is at least equivalent to the number ofreactive groups of the polyester. The reaction is carried out until thedesired reduction of the melt index is achieved.

Representative polyfunctional compounds are di- and poly-isocyanates,epoxides and poly-epoxides, and the dianhydrides of tetracarboxylicacids.

Preferred compounds are di-isocyanates such as hexamethylenediisocyanate, dianhydrides of aromatic tetracarboxylic acids, andpoly-epoxides.

The upgrading of the polyester can be obtained by extruding thepolyester in the presence of the upgrading agent.

It is also possible to prepare polyesters having the desired melt-indexand molecular-weight characteristics directly by polycondensation, aslong as the viscosity values of the melt are not too high.

The polyesters usable for the preparation of the compositions of theinvention are obtained from aliphatic polyesters comprising, in thechain, repeating units derived from an aliphatic dicarboxylic acid orfrom a hydroxy-acid with more than two carbon atoms.

The polyester are preferably selected from the same a) and b) groups ofpolyesters set forth for the A) type compositions.

The polyesters, particularly those obtained from hydroxy-acids, may bemodified to form block copolymers or graft copolymers with polymers orcopolymers which can react with the carboxyl and/or hydroxyl groupspresent in the polyesters.

The homopolymers and copolymers of epsilon-hydroxy-acids, particularly6-hydroxy-caproic acid and the corresponding lactone are preferred. Thepolycaprolactone preferably has a mean viscosimetric molecular weightgreater than 100,000 and R-ratio values preferably of between 35,000 and110,000.

The polyesters and their derivatives generally have melting points ofbetween 40° and 175° C. and molecular weights (viscosimetric mean)greater than 20,000, preferably greater than 40,000.

The polyesters and their derivatives can advantageously be used inmixtures with one or more polymers or copolymers obtained fromethylenically unsaturated monomers, containing polar groups, preferablyhydroxyl and carboxyl groups, such as ethylene/vinyl acetate,ethylene/vinyl alcohol and polyvinyl alcohol copolymers (the latterobtained by hydrolysis of polyvinyl acetate and ethylene vinyl acetatecopolymers with degrees of hydrolysis of from 50 to 100%) andethylene/acrylic acid copolymers.

The ethylene/vinyl alcohol copolymers preferably contain from 10 to 50%by weight of ethylene.

The alcohol groups of the polymers mentioned above may be converted intoether, ester, acetal or ketal groups.

Preferred mixtures contain poly-epsilon-caprolactone and ethylene/vinylalcohol or ethylene/vinyl acetate copolymers.

The ratio by weight between the polyesters and the polymers orcopolymers containing alcohol groups is preferably between 1:6 and 6:1,more preferably between 1:4 and 4:1.

The ratio by weight between thermoplastic starch and polyester isgenerally between 1:10 and 10:1 and is selected in a manner such thatthe polyester constitutes the continuous phase and the starch thedispersed phase.

The compositions of the invention preferably comprise a plasticizergenerally selected from polyols containing 3 or more carbon atoms and 2or more alcohol groups such as glycerol, di- and polyglycerols, ethyleneor propylene glycol, ethylene or propylene diglycol, polyethyleneglycol, polypropylene glycol, 1,2-propandiol, trimethyl propane,pentaerythritol, sorbitol, erythritol, xylitol, sucrose, 1,3-propandiol,1,2-, 1,3-, 1,4-butandiol, 1,5-pentandiol, 1,6-, 1,5-hexandiol, 1,2,6,-,1,3,5-hexantriol, neopentyl glycol.

The polyols indicated above may be used in the form of etherification oresterification products, such as polyol acetates, ethoxylates andpropoxylates, particularly sorbitol ethoxylate, glycerol ethoxylate,sorbitol acetate, and pentaerythritol acetate.

The quantities of plasticizers used are generally from 1 to 100%,preferably from 10–30% by weight, relative to the starch.

The use of plasticizers of this type is described in U.S. Pat. No.5,292,782, the description of which is incorporated herein, byreference.

The compositions may also comprise the interfacial agents described forthe A) compositions. In this case, the use of the interfacial agentfurther improves the rheological characteristics of the compositions.

The thermoplastic starch present in the composition is obtained fromnative starch extracted from vegetables such as potatoes, rice, tapioca,maize and/or from chemically or physically modified starch.

The compositions of the invention may include quantities of from 0.5 to20% by weight of urea or hydroxides of alkaline-earth metals, between0.1 and 5% of inorganic salts of alkali-metals or alkaline-earth metals,particularly LiCl, NaCl, Na₂SO₄, and also compounds containing boron,particularly boric acid, proteins such as casein, gluten, salts ofproteins, abietic acid and derivatives thereof, rosinic acids, andnatural gums.

Other hydrophobic polymers such as polyethylene, polypropylene andpolystyrene and additives such as anti-oxidants, lubricants,flame-proofing agents, fungicides, herbicides, fertilizers andopacifiers, compounds with rodent-repellent effects, and waxes may bepresent.

The compositions are preferably prepared by mixing the components in anextruder heated to a temperature of between 100° and 220° C.

Instead of an extruder, the components may be mixed in any apparatuswhich can ensure temperature and shear-strain conditions correspondingto the viscosity values of the thermoplastic starch and of the polymerincompatible with starch.

The starch may be treated to render it thermoplastic before being mixedwith the other components of the composition or during the mixing of thecomponents of the composition.

In both cases, known methods are used, with operating temperatures ofbetween about 100° and 220° C., in the presence of plasticizers andpossibly water.

The water content at the output of the extruder (that is, before anyconditioning treatments) is preferably less than 5% by weight, and maybe almost zero.

The content is regulated by degassing during extrusion or with the useof dehydrated starch with a low water content.

The use of polyesters having the molecular-weight and melt-indexcharacteristics indicated above, possibly in combination with the agentswith interfacial effect and a) and e) type used in A) compositions,gives rise to compositions which have a fine microstructure of thedispersed phase in which more than 80% of the particles have dimensionsof less than 1 micron and the numeral average particle size is between0.1 and 1 micron.

The B) compositions, similarly to the A) compositions, are usableparticularly in the preparation of films, sheets, fibres, ininjection-moulding, thermoforming, coextrusion, and in the preparationof expanded materials.

Fields of use of particular interest are those of nappies and sanitarytowels, of films for agriculture, of bags, of films for cellophaning, ofdisposable articles, and of expanded packaging elements.

The films may be used in laminates with layers formed by polyesters,polyester-amides, polyamides, aliphatic polycarbonates,aromatic/aliphatic polycarbonates, soluble polymers such as polyvinylalcohol or other polymers, with paper, or with layers of inorganicmaterials such as silica, aluminium, etc.

The compositions may be supplemented with fillers, preferably of naturalorigin, and with natural or modified resins such as abietic acid.

The C) compositions are characterised in that they comprise a polyesterselected from the group consisting of aliphatic aromatic copolyesters,polyester-amides, polyester-ethers, polyester-ether-amides,polyester-urethanes and polyester-ureas, and in that they are obtainedby extrusion under conditions wherein the content of water is maintainedhigher than 1% up to 5% by weight during the mixing of the components(content measured at the exit of the extruder i.e. prior to anyconditioning treatment).

From the state of the art, particularly from WO93/07213 with describescompositions comprising starch and a copolyester obtained from mixturesof a terephthalic acid and adipic or glutaric acid and from an aliphaticdiol, wherein the components are accurately dried, before being mixed,to a water content less than 1 wt. and from WO96/31561 which describescompositions comprising starch and copolyesters such asaliphatic-aromatic copolyesters, polyester-amides andpolyester-urethanes, wherein starch is a plasticized product dried to acontent of water less than 1% wt. or the copolyester-starch mixture isblended in the extruder under conditions to maintain the water contentless than 1% wt, the expected result of mixing in the melt at hightemperatures and in the presence of water at a level higher than 1% byweight a copolyester of the type above mentioned was a remarkablehydrolysis and degradation of the copolyester with consequent impairmentof the properties of the final product.

Contrary to the expectations, it has been found that operating under theconditions used to prepare the compositions C), the decrease of themolecular weight of the polyester is negligible.

It has further been found that, if the compatibilisation conditionsduring the mixing with extruder are good enough to obtain a dispersionof starch in form of particles having an average size less than 1micron, preferably less than 0,5 micron, the resulting compositionspresent properties similar to those of polyethylene and which remainpractically unchanged under relative low humidity conditions.

Another aspect which is characteristic of the compositions C) resides inthat by extruding the compositions under the above specified humidityconditions i.e. a water content from 1 to 5% wt. it is possible toobtain products endowed with a microstructure finer than that obtainableby extruding, all the other conditions being the same, compositionswherein the polymeric hydrophobic component is a polyester totallyaliphatic in its structure.

With the compositions C), the use of an interfacial agent as specifiedfor the compositions A) and of a polymer with a molecular wight and meltindex modified as set forth for the compositions B) is an optionalcondition.

When the interfacial agent and/or the modified polymer is used, therheological properties of the compositions are further improved.

The aliphatic-aromatic copolyesters preferably are of the random type.Block copolymers can also be used.

The copolyesters are obtained by polycondensation, according to knownmethods, of mixtures of an aliphatic dicarboxilic acids such as adipicsebacic, succinic, azelaic or glutaric acids and/or a hydroxy acid withmore than 2 carbon atoms or the corresponding lactone with an aromaticdicarboxilic acid such as terephthalic and isophthalic acids with a diolwith 1–20 carbon atoms, such as 1,2-ethanediol, 1,3-propandiol,1,4-butandiol, 1,4-cyclohexandimethylol.

The copolyesters have in general formula:(—CO—R—CO—OG—O)_(a)—(CO—Q—O)_(b),wherein up to about 40% by mols of R is a bivalent non-aromatic radicalC₁–C₁₂ and the remaining of R is a p-phenlene radical; G is up to 30% bymols a radical selected from —(CH₂)₂—O—(CH₂)₂, —(CH₂)₂—O—(CH₂)₂—O—(CH₂)₂the remaining of G being an ether-polyalkylenic radical with molecularweight higher than 250 or a radical (CH₂)₂—O—(CH₂)₄; Q derives from ahydroxyacid with more than 2 carbon atoms; a) and b) are molar fractionsof the polymer with a) being comprised from 0.6 and 1 and b) from 0 to0,4.

Copolyesters of the above type are described in U.S. Pat. No. 5,446,079and WO 93/07123 which are herein incorporated by reference.

The polyester-amides have in general a structure deriving for 30–70% byweight from an aromatic or aliphatic-aromatic ester and from 70–30% froman aliphatic amide.

Examples of polyester-amides arepoly-epsilon-caprolactone-epsilon-caprolactam,poly-alkylenadipate-epsilon-caprolactam.

Examples of usable polyester-amides are described in EP-A-641817 and inWO96/21689, WO-96/21690, WO-96/21691 and WO-96/21692, the description ofwhich is herewith incorporated by reference.

The polyester-ether copolymers can be obtained from an aromaticdicarboxylic acid such as terephthalic acid and a polyalkylenoxide.

The polyester-urethane and polyester-urea copolymers can be obtainedaccording to known methods; for instance the polyester-urethanes from adicarboxilic acids such as terephthalic acid and an aliphaticdiisocianate.

The compositions C) comprise from 20 to 95% by weight of starch and5–80% by weight of copolyester. Preferably the content of starch is from30 to 75% by weight.

The copolyesters can be used in mixtures with the polymers andcopolymers containing polar groups as specified for the compositions A)and B).

The weight ratio between the copolyester and the (CO) polymer containingpolar groups is the same as specified for A) and B) compositions.

The thermoplastic starch present in the compositions is obtained fromnative starch or chemically or physically modified starch as describedfor the compositions B). The compositions preferably contain aplasticizer of the type as specified in the compositions A) and B) withamounts therein disclosed.

The compositions may contain additives as set forth for the compositionsA) and B).

The composition are prepared by extrusion of the components underconditions that the content of water during the mixing stage ismaintained, by degassing, at values from 1 to 5% by weight.

The content of water of the native starch can be comprised from 1 to 16%by weight.

The extrusion conditions (temperature which can range from 100° to 220°C. and shearing forces) are selected as to obtain a goodcompatibilisation between starch and the incompatible copolyester.

The starch may be treated to render it thermoplastic according to theknown method e.g. operating in the presence of plasticizers and water,before being mixed with the components of the composition or during themixing.

The compositions are useful for the same applications, as disclosed forthe compositions A) and B).

Thanks to the rather high melting point of the copolyesther used in thecompositions C), the same are particularly usable in applicationswherein a food thermal resistance is required.

The following examples 1–45 (examples 1, 42 and 44 are comparisonexamples) are provided by way of non-limiting illustration of A)compositions of the invention, examples 1A–6A and comparative examples1A–2A by way of non-limiting illustration of B) compositions; andexamples 1B and 2B of C)-compositions.

The esters used in the examples 1–45 were prepared in accordance withconventional methods. In the case of the stronger carboxylic acids, theuse of acid catalysts was not necessary but it sufficed to remove thewater produced by the reaction. For the weaker acids, particularly thefatty acids, the reaction was catalyzed with small amounts of toluenesulphonic acid.

Since the esterification did not affect all of the hydroxyl groups ofthe polyol (so that both ester functions and alcohol functions werepresent simultaneously in the reaction product) but only a fraction ofbetween 10 and 90% of the hydroxyl groups, preferably between 20 and70%, and more preferably between 25 and 50%, it was possible to continuethe reaction until the acid was used up. Any traces of unreacted acidcould be neutralized with organic or inorganic bases, preferablytriethanolamine.

The product of these partial esterifications was constitutedpredominantly by the polyol with the desired degree of esterification;the second largest fraction was constituted by unsubstituted polyol, andthe remainder was constituted by polyol with higher degrees ofsubstitution or, in the case of dicarboxylic acids, by oligomeric forms.

The inherent viscosity given in the examples 1A–6A is expressed by theequation:

${\lbrack\eta\rbrack{inh}} = \frac{\lbrack\eta\rbrack{t/t}\mspace{14mu}{^\circ}}{c}$

-   -   where:

t°=time taken by a known volume of pure solvent to pass through thecapillary of the viscosimeter;

t=time taken by an identical volume of the solution containing thepolymer to pass through the capillary, c=concentration of the polymer inthe solution, expressed in g/dl.

The instrument used for the measurements was a Bischoff viscosimeter.

The measurement was carried out in tetrahydrofuran at 25° with the useof 1 g of polymer in 100 ml of solvent.

In the following examples all “parts” are intended by weight, unlessotherwise stated.

EXAMPLE 1 (COMPARISON)

A composition containing 55 parts of PCL TONE 787 (Union Carbide), 31parts of Globe maize starch 03401 (Cerestar), 0.25 parts of erucamide,12 parts of glycerol, and 1.75 parts of water was mixed in an OMCsingle-screw extruder D=20 mm and L/D=30 with an operating temperatureprofile of 80/180/150/130° C. at 70 rpm.

The pellets obtained were then supplied to a Haake single-screwextruder, D=19 mm and L/D=20, with a film-forming head.

The heating profile during the blow-moulding was 115/120/125/130° C. at30 rpm.

The film obtained constituted the reference material.

EXAMPLES 2–40

The compositions given in the following table were mixed and filmed withthe use of the method of Example 1 and with the PCL, starch, water anderucamide parts remaining the same but with all or some of the glycerolreplaced by the esters indicated below:

TABLE 1 Example 2 3 4 5 6 7 8 9 10 11 12 13 14 glycerol 9 9 9 6 9 6 5 55 6 6 6 11 chloro- 3 acetate tri- 3 chloro- acetate pivalate 3 6 2 3caproate 3 6 5 4 1,5 6 caproate laurate 6 S-oleate 3 S-oleate 6 oxalate1 Example 15 16 17 18 19 20 21 22 23 24 25 26 27 glycerol 9 7 — 4 2 9 69 9 — 6 9 6 sorbilene 4 4 oxalate 3 5 12 4 6 1 S-oxalate 3 6 TMP- 3oxalate EG- 3 12 oxalate caproate 5 malonate 3 6 Example 28 29 30 31 3233 34 35 36 37 38 39 40 glycerol — 9 9 — 9 5 7 9 9 6 6 9 6 malonate 12maleate 3 succinate 3 12 adipate 3 azelate 7 suberate 7 acetyl 3 citrateoleate 3 6 nonyl- 6 phenol 10 nonyl- 3 6 phenol 19Note

Glycerol and sorbilene are polyols used as plasticizers; sorbilene is asorbitol monoethoxylate.

Unless expressly indicated, the ester was obtained by the reaction of aCOOH function with one mole of glycerol.

-   caproate 1,5 resulted from the reaction of 1.5 moles of caproic acid    per mole of glycerol-   S-oleate was monosorbitane oleate-   S-oxalate was produced from one mole of oxalic acid and two moles of    sorbitol-   TMP-oxalate was produced from one mole of oxalic acid and two moles    of trimethylol propane-   EG-oxalate was produced from one mole of oxalic acid and two moles    of ethylene glycol-   nonylphenol 10 was nonylphenol ethoxylate with 10 moles of ethylene    oxide; HLB=13-   nonylphenol 19 was nonylphenol ethoxylate with 19 moles of ethylene    oxide; HLB=16    Evaluation of the Material Samples

The films were conditioned at 20° C. and 15′ RH for 48 hours and werethen subjected to preliminary tear-strength screening. The evaluationwas carried out manually and the appraisal was as follows:

Example very good good poor very poor 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9x 10 x 11 x 12 x 13 x 14 x 15 x 16 x 17 x 18 x 19 x 20 x 21 x 22 x 23 x24 x 25 x 26 x 27 x 28 x 29 x 30 x 31 x 32 x 33 x 34 x 35 x 36 x 37 x 38x 39 x 40 xPaper Contact Test

The formulations which gave good or very good responses in thepreliminary screening were tested in terms of tear strength after thecorresponding films had been placed between sheets of pure cellulosepaper at 50° C. and RH<10% for two months.

In this case, preliminary manual screening was again carried out.

The test was quite severe since the paper was able to take plasticizerssuch as glycerol from the films.

The results were as follows:

Example very good good poor very poor 1 x 2 x 3 x 5 x 7 x 8 x 9 x 10 x11 x 12 x 13 x 14 x 15 x 16 x 17 x 18 x 19 x 20 x 21 x 22 x 23 x 24 x 25x 26 x 27 x 28 x 30 x 31 x 32 x 33 x 34 x 37 x 38 x 40 xTear Strength after the Films Had Been Washed in Water

This was the most severe test since the conventional plasticizers(glycerol and sorbilene in this case) as well as the water-solubleesters were completely removed.

In practice, the film was immersed in distilled water for 24 hours,after which it was left to dry for 25 hours at ambient temperature.

The films which were good or very good in the paper contact test weresubjected to this test; evaluation was again manual.

Example very good good poor very poor 1 x 2 x 3 x 5 x 7 x 8 x 9 x 10 x11 x 12 x 13 x 14 x 15 x 16 x 17 x 18 x 19 x 20 x 21 x 22 x 23 x 24 x 25x 26 x 27 x 28 x 30 x 31 x 33 x 34 x 37 x 38 x 40 xMechanical Properties

The mechanical properties of some films subjected to washing with waterare given in comparison with the untreated films.

Example Sigma b Ext.* Modulus Breaking energy No. MPa % MPa KJ/m² 1untr. 33 849 200 6837 1 washed 19 3 1179 16 7 untr. 12 684 156 3958 7washed 8 314 752 1790 12 untr. 22 969 271 6409 12 washed 12 8 751 45 13untr. 23 946 161 6340 13 washed 11 326 573 1768 17 untr. 33 923 170 751517 washed 19 490 885 4750 18 untr. 33 849 200 6837 18 washed 19 420 9964970 19 untr. 26 741 170 5042 19 washed 17 393 1007 3339 36 untr. 251076 156 7582 36 washed 10 9 804 38 37 untr. 23 946 161 6349 37 washed 6326 546 1768 *Ext. = elongation at break

EXAMPLE 41

A composition containing 55 parts of PCL Tone 787, 31 parts of Globemaize starch 03401 (Cerestar), 6 parts of oxalic acid monoglyceride, 3parts of glycerol, and 5 parts of sorbitol monoethoxylate was mixed inan extruder as in Example 1 and then filmed. The film was then subjectedto the water washing test. The tensile properties, compared with thesame film which had not been washed, were as follows:

Sigma b Ext. Modulus Breaking energy MPa % MPa KJ/m² untr. 28 760 2346321 film washed 23 733 310 5870 film

EXAMPLE 42 (COMPARISON)

A composition containing 44 parts of cellulose acetate with a degree ofsubstitution DS=2.5, 16 parts of diacetin, 32.8 parts of maize starch,0.2 parts of erucamide and 8 parts of Sorbilene was mixed in a 30 mmAPV-2030 XLT extruder with two screws and L/D=35+5. The heating profilewas as follows: 60/100/180×14° C. and RPM=170.

The extruded material was pelletized and was pressure moulded at 190° C.to give test pieces 2 mm thick. A test piece was broken cold in order toinvestigate the fracture surface.

EXAMPLE 43

Using the method of Example 42, a similar composition was prepared butwith the Sorbilene replaced by oxalic acid monoglyceride. The materialwas pressure moulded as in Example 42.

The mechanical properties compared were as follows:

Example 42 Example 43 Sigma b MPa 22 20 Ext. % 6.6 6.6 Modulus MPa 22312121 Breaking energy KJ/m² 67.7 69.4 MFI g/10′ 0.17 4.65 Spiral cm 557900

As can be seen, the use of the ester considerably fluidized thecomposition in both MFI and spiral terms, for given tensile properties.The effect in bringing about compatibility was even clearer from SEMmorphological analysis of the fracture surfaces, from a comparison ofwhich, the material containing the ester was clearly more homogeneous.

MFI was measured at 170° C. with a load of 5 kg.

EXAMPLE 44 (COMPARISON)

A composition exactly the same as that of Example 1 except that the PCLwas replaced by a random aliphatic-aromatic copolyester obtained from60:40 butylene adipate/butylene terephthalate was prepared with the useof the method described in Example 1.

The material was filmed and characterized.

EXAMPLE 45

Example 44 was repeated with the introduction of 5 parts of malonic acidmonoglyceride instead of the same quantity of glycerol.

The material was filmed and characterized.

The tensile properties compared were as follows:

Example 44 Example 45 Sigma b MPa 6 22 Ext. % 408 788 Modulus MPa 91 79Breaking energy KJ/m² 1432 3780

COMPARATIVE EXAMPLE 1A

200 g of epsilon-caprolactone, 3.8 mg of tin octanoate, and 186 mg of1,4 butandiol were loaded into a 300 ml glass reactor and heated to 180°C. for 24 hours with stirring and in an atmosphere of nitrogen.

The polymer obtained has the following characteristics:

Inherent viscosity 1.42 dl/g MW (viscosimetric) 125000 MI 5.0

EXAMPLE 1A

Comparative example 1A was repeated but with 105 mg of 1,4 butandiolinstead of 186 mg.

The polymer obtained had the following characteristics:

Inherent viscosity 1.75 dl/g MW (viscosimetric) 183000 MI 1.8

EXAMPLE 2A

253.3 g of Union Carbide PCL Tone 787, dried under vacuum at 50° C. for24 hours, was placed in a 800 ml glass reactor and heated to 180° C.with stirring (100 RPM).

When the temperature had been reached, 1.0 ml of 1,5 hexamethylenedi-isocyanate was added and the reaction was continued for two hours.

The characteristics of the starting PCL and of the reaction product wereas follows:

PCL Tone 787 Example 2A Inherent viscosity 1.28 dl/g 1.38 dl/g MW(viscosimetric) 108000 121000 MI 7.0 2.5

EXAMPLE 3A

A composition containing 99.8 parts of PCL Tone 787, dried as in Example2A, and 0.4 parts of 1,6-hexamethylene di-isocyanate was supplied to anOMC twin screw extruder, L/D=36 and D=60 mm, operating under thefollowing conditions:

-   -   temperature profile: 20/90/90/140/175/190×4/170/150° C.    -   flow-rate: 10 kg/h    -   RPM: 150

The extruded and pelletized material had the following characteristics:

Inherent viscosity 1.35 dl/h MW (viscosimetric) 118000 MI 2.9

EXAMPLES 4A–6A, COMPARATIVE EXAMPLE 2A

The following compositions:

Example 2A (comp) 4A 5A 6A PCL Example 1A (comp)    49% — — — PCLExample 1A —    49% — — PCL Example 2A — —    49% — PCL Example 3A — — —   49% Maize starch 36 36 36 36 Glycerol 12 12 12 12 Water  3  3  3  3were mixed in an OMC single-screw extruder L/D=30 and D=20 mm operatingwith a 80/180/150/130 temperature profile at 70 RPM.

The pellets obtained were then supplied to a Haake single-screwextruder, L/D=20 and D=19 mm with a filming head; the temperatureprofile during the blow-moulding was 115/120/12525/130 and the RPM=30.

The films obtained, which were about 40 microns thick, werecharacterized from the point of view of their tensile properties and oftheir tear strength. The measurements were made with test samplesconditioned at 50% and 20% RH.

In particular, with regard to the tear strength, measurements were madeat both low and high speed; in the first case, an Instron instrument wasused with a speed of 250 mm/min, in accordance with ASTM D-1938; in thesecond case an Elmendorf pendulum was used in accordance with ASTM-1922.

Example 2Acomp. 4A 5A 6A Sigma b (MPa) 10 20 10 18 9 18 10 18 Ext. (%)830 185 820 530 595 535 605 570 Elas. Modulus 205 975 235 780 135 735170 710 (MPa) Breaking 83 30 91 91 107 116 97 94 energy (MJ/m³) Tearstrength 1 97 83 89 85 87 90 87 85 (N/mm) Tear strength 2 200 7 150 150180 128 170 135 (N/mm) Tear strength 1 = low speed Tear strength 2 =high speed

For each example, the data for 50% and 20% relative humidity are given(with 50% in the first column).

EXAMPLE 1B

54 parts of a Eastman Chemical 14766 copolyester (based on terephthalicacid, adipic acid and butandiol), 33.4 parts of maize starch CerestarGlobe 03401, 5.8 parts glycerol and 6.5 parts water were fed to atwin-single screw extruder APV V30 mod. 2030 operating under thefollowing conditions:

-   -   standard screws (residence time 80 seconds);    -   screw diameter: 30 mm    -   L/D: 10    -   RPM: 1790    -   Thermal profile: 60/100/180×14° C.    -   Active degassing

The obtained pellets had water content of 1.18% by weight.

Upon having removed the starch by solubilization with HCl 5 M, theaverage numerical dimensions of the dispersed starch phase wasdetermined by SEM and was comprised within 0.3 and 0.5 μm.

The intrinsic viscosity of the polyester, recovered by extraction withCHCl₃ was:

[η]=0.86 dl/g in CHCl₃ at 30° C. against [η]=0,93 dl/g of the startingpolymer.

The pellets were subjected to film blowing in a Haake singlescrewextruder, having a diameter of 19 mm, L/D=20 at 140° C., thereby toobtain a film having a thickness of about 45 μm.

The mechanical properties of the obtained films are shown in thefollowing table:

σy εy σb εb Mod Energy Mpa % Mpa % Mpa KJ/m² 5.7 9.1 7.4 478 161 1566

EXAMPLE 2B

Example 1B was repeated by substituting the standard screws by screwsincluding back mixing (reverse) sections. In this case, the residencetime in the extruder was raised to 130 seconds.

The pellets were examined according to Example 1B and the followingresults were obtained:

Water: 1.76% by weight

Particle dimensions comprised within 0.3 and 0.4 μm

Polyester viscosity after blending: [η]=0.83 dl/g

The pellets were subjected to film blowing according to Example 1B.

The mechanical properties of the films were the following:

σy εy σb εb Mod Energy Mpa % Mpa % Mpa KJ/m² Film as such 7.3 13.5 12.6784 154 3476 Washed film (*) 9.0 14.6 6.7 550 198 2501 (*) theplasticizers were removed from the film by emulsion in water for 24hours

The same washed film, conditioned at 23° C. and 20% RH, had a tearstrength of 139 KJ/m² at a speed of 1 m/sec.

The pellets were finally processed in an extruder having a flat head toobtain a sheet having a thickness of 6000 μm; the sheet was foundsuitable for thermoforming.

1. A biodegradable heterophase polymeric composition having goodresistance to ageing and to low humidity conditions, the compositioncomprising a thermoplastic starch a thermoplastic polymer incompatiblewith starch, wherein the starch is in a dispersed phase and thethermoplastic polymer is in a continuous phase, and an interfacial agentwhich is an ester having an hydrophilic/lipophilic balance index value(HLB) greater than 8, which ester is obtained from a polyol or a mono-or polycarboxylic acid having a dissociation constant pK lower than 4.5,wherein the pK value refers to the first carboxyl group of thepolycarboxylic acid.
 2. The composition according to claim 1, wherein inthe polyol portion of the ester comprises 3 or more carbon atoms and 2or more alcohol groups.
 3. The composition according to claim 2, inwhich the polyol is glycerol.
 4. The composition according to claims 2or 3, in which the ester is a monoglyceride.
 5. The compositionaccording to claim 2, in which the ester is an ester of oxalic, malonic,succinic, adipic, glutaric, maleic, citric, tartaric, lactic, or mono-di-, or tri-chloroacetic acid.
 6. The composition according to claim 5,in which the ester is on average the monoglyceride.
 7. The compositionaccording to claim 1, in which the ratio by weight between thethermoplastic starch and the thermoplastic polymer incompatible withstarch is such that the starch constitutes the dispersed phase and thethermoplastic polymer constitutes the continuous phase.
 8. Thecomposition according to claim 1, in which the quantities of the estersused are from 0.5 to 20% by weight relative to the total composition. 9.The composition according to claim 1 further comprising a plasticizer.10. The composition according to claim 9, in which the plasticizer isselected from polyols with 3 or more carbon atoms and with 2 or morealcohol groups.
 11. The composition according to claim 10, in which thepolyol is selected from glycerol, sorbitol, etherified or esterifiedsorbitol, ethyleneglycol and trimethylolpropane.
 12. The compositionaccording to claim 9, in which the plasticizer is present in thecomposition from 1 to 100% by weight relative to the starch.
 13. Thecomposition according to claim 1, in which the ester is present in thecomposition in a ratio of from 1:30 to 1:2.5 by weight to the starch.14. The composition according to claim 1, in which the thermoplasticpolymer is an aliphatic or aliphatic-aromatic polyester, which isobtained by a reaction selected from a polycondensation of hydroxyacidswith 2 or more carbon atoms, or from the corresponding lactones orlactides, a polycondensation of a diol with 1–12 carbon atoms with adicarboxylic aliphatic acid or with mixtures thereof with dicarboxylicaromatic acids.
 15. The composition according to claim 14, in which thepolymer is a poly-ε-caprolactone.
 16. A film produced from a compositionof claim
 1. 17. A consumer product comprising a film according to claim16, wherein the consumer product is selected from the group consistingof nappies, sanitary towels, bags, laminated paper, laminates and filmstreated with inorganic products.
 18. Compositions comprising a filmaccording to claim
 16. 19. The composition according to claim 10 whereinthe polyol is etherified or esterified.